The overall goal of our research is to elucidate the role of macrophages and inflammatory mediators in acute and chronic pulmonary injury induced by vesicants with the long-term objective of identifying targets for therapeutic intervention. We hypothesize that macrophages play a dual role in the pulmonary toxicity of vesicants. Whereas initially classically activated M1 macrophages contribute to acute tissue injury by releasing excessive quantities of proinflammatory/cytotoxic mediators, subsequent release of mitogenic and fibrogenic mediators by overactive M2 macrophages leads to chronic injury including pulmonary fibrosis. Using sulfur mustard and nitrogen mustard as model vesicants, plans are to determine if M1 and M2 macrophage subpopulations differentially contribute to the acute and long-term consequences of vesicant intoxication, and if pharmacologically modifying their activity or mediators they release mitigates toxicity. Working with the Medicinal Chemistry and Pharmaceutics Core, we also plan to engineer and evaluate an injectable lung delivery system consisting of poly(ethylene glycol) hydrogel particles (gel particles or GPs) to target hyperactive M1 lung macrophages and cytotoxic/proinflammatory mediators released following vesicant exposure. If successful, our studies will provide a strategy for treating not only sulfur mustard and nitrogen mustard-induced lung toxicity, but other chemical threat agents that induce pulmonary injury including chlorine, phosgene and ammonia, as well as other pulmonary pathologies associated with inflammation.